Indirect Evaporative Cooler Control With Liquid Desiccant Dehumidification
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Solution Overview
Problem
Conventional evaporative coolers are limited in their ability to provide adequate cooling, especially in high temperatures and humid environments, and they require significant maintenance due to mineral deposits and humidity issues, making them unsuitable for widespread commercial and residential use without significant improvements.
Innovation Solution
A control method for an indirect evaporative cooling system that uses a liquid desiccant dehumidifier and airflow control to maintain temperature and humidity levels, incorporating a permeable membrane to separate liquid desiccant from air, reducing maintenance needs and enhancing cooling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If conventional evaporative coolers are used to provide cooling, then operating cost is reduced, but cooling effectiveness is insufficient in high temperature and humidity environments
Solution Approach 1:
The system is divided into two independent stages: a direct evaporative cooling stage followed by a refrigerated cooling stage. This segmentation allows each stage to perform its optimal function - the first stage provides preliminary cooling with low operating cost, while the second stage ensures adequate cooling effectiveness in high temperature environments, resolving the contradiction between operating cost and cooling effectiveness.
Solution Approach 2:
The direct evaporative cooler performs preliminary cooling of the ambient air before it enters the refrigerated cooler. This preliminary action reduces the temperature and humidity of the air entering the second stage, allowing the refrigerated cooler to operate more efficiently and achieve adequate cooling effectiveness while maintaining lower overall operating costs.
2Temperature
If conventional evaporative coolers operate in high temperature environments, then cooling demand is met, but maintenance requirements increase due to mineral deposits
Solution Approach 1:
The system extracts and removes a portion of the air stream (purge air) after it has passed through the evaporative cooling pads. This extracted air is used to prevent excessive mineral deposit accumulation on the pads by periodically removing concentrated mineral-laden air, thereby reducing maintenance requirements while maintaining cooling capability in high temperature environments.
Solution Approach 2:
The system discards a controlled portion of the air stream that has picked up mineral deposits during evaporation. By purging this contaminated air, the system prevents excessive mineral buildup on the cooling pads, reducing the frequency of cleaning and maintenance while preserving the cooling effectiveness in high temperature conditions.
3Ease of manufacture
If conventional evaporative coolers are installed, then initial cost is reduced, but system complexity increases due to additional components required
Solution Approach 1:
The refrigerated cooler unit is designed to serve multiple functions: it provides the primary refrigerated cooling, handles the air stream management, and incorporates the purge function to prevent mineral deposits. This multi-functionality reduces the need for separate dedicated components, thereby managing system complexity while maintaining the low initial cost advantage of combining evaporative and refrigerated cooling.
Solution Approach 2:
The system merges the evaporative cooling function and refrigerated cooling function into a single integrated unit with shared components such as the air handler, controls, and housing. This combining approach reduces overall system complexity compared to having completely separate systems, while still maintaining the cost advantages of using an evaporative cooler as the first stage.
4Device complexity
If conventional evaporative coolers are used, then simplicity of design is maintained, but adaptability to different climates is limited
Solution Approach 1:
The system incorporates variable speed controls on the fans and refrigeration compressor that allow the unit to dynamically adjust its operation based on ambient temperature and humidity conditions. This dynamic capability enables the simple dual-stage design to adapt to different climates - operating primarily in evaporative mode in dry climates and switching to more refrigerated cooling in humid or high-temperature climates.
Solution Approach 2:
The system changes operational parameters such as fan speeds, refrigeration cycle parameters, and purge rates based on ambient conditions. This parameter adjustment allows the relatively simple dual-stage design to adapt to different climate conditions, maintaining design simplicity while achieving climate versatility through intelligent control of operating parameters.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively cools and dehumidifies air simultaneously, reducing system size and cost, and eliminates maintenance issues associated with mineral deposits, providing a more efficient and reliable cooling solution for commercial and residential applications.
Implementation Method 1
incorporating a permeable membrane to separate liquid desiccant from air
Implementation Method 2
evaporative coolers are devices that use simple evaporation of water in air to provide cooling
Implementation Method 3
use the latent heat of evaporation to create cool moist air
Implementation Method 4
liquid desiccant dehumidifier and airflow control to maintain temperature and humidity levels
Data Source
AI summary
A control method for operating an indirect evaporative cooler to control temperature and humidity. The method includes operating an airflow control device to provide supply air at a flow rate to a liquid desiccant dehumidifier. The supply air flows through the dehumidifier and an indirect evaporative cooler prior to exiting an outlet into a space. The method includes operating a pump to provide liquid desiccant to the liquid desiccant dehumidifier and sensing a temperature of an airstream at the outlet of the indirect evaporative cooler. The method includes comparing the temperature of the airstream at the outlet to a setpoint temperature at the outlet and controlling the pump to set the flow rate of the liquid desiccant. The method includes sensing space temperature, comparing the space temperature with a setpoint temperature, and controlling the airflow control device to set the flow rate of the supply air based on the comparison.